Malignant and benign growth of the prostate gland typically cause urinary problems. Benign prostate hyperplasia (BPH) is a benign growth within the prostate gland which causes an obstruction that constricts the urinary canal or prostatic urethra, thereby restricting urine flow and making urination difficult, painful, or in aggravated circumstances, almost impossible. At various levels of severity, BPH afflicts a significant percentage of the older male population. Malignant cancer of the prostate gland may also create similar urination problems, but more significantly, malignant prostate cancer may spread to other tissues unless eradicated.
Thermotherapy is a treatment where bodily tissue is subjected to heat at a temperature high enough for a long enough period of time to cause tissue death or necrosis while coagulating blood flow into the dead tissue. In the treatment of BPH, thermotherapy is used to kill a limited amount of the prostate gland surrounding the prostatic urethra, without destroying the entire prostate gland. As the dead tissue sloughs off after treatment and the prostatic urethra grows back, a larger urinary canal exists through the prostate gland to permit urine flow without obstruction or significant pain. In the treatment of malignant prostate gland cancer, it is desirable for the thermotherapy to kill only the malignant cancerous tissue, while preserving the adjoining healthy tissue.
Typical sources of heat used for prostate thermotherapy include microwave radiation, radio frequency energy, laser energy, and hot liquid. Microwave energy is a very effective thermotherapy energy source for treatment of prostate gland disease. The microwave energy is delivered from a microwave antenna located adjacent to the prostate gland. The microwave antenna is connected by a microwave feed cable to a microwave generator. The microwave generator supplies the energy through the coaxial cable to the antenna, and the energy radiates from the antenna into the adjoining tissue. The tissue is heated in accordance with the amount of microwave energy delivered from the antenna and the pattern of radiation emitted from the antenna, called the specific absorption rate or SAR.
The quality of the thermotherapy treatment, and the physiological outcome from the treatment, is greatly enhanced by providing usable information concerning the degree of heat treatment and the progress of tissue necrosis during the treatment. The assignee of the present invention has developed a prostatic treatment catheter which permits a temperature probe containing temperature sensors to be inserted into the prostate gland and the adjoining tissue. This type of urinary catheter is described in U.S. reissue Pat. No. Re 38,299. The temperature information obtained from within the treated and adjoining tissue is interpreted and processed to inform the surgeon of the progress and degree of tissue necrosis during the treatment. U.S. Pat. No. 6,445,957, also assigned to the assignee hereof, describes more about interpreting and presenting the information from the temperature sensors inserted into the tissue.
To obtain the most reliable information concerning the extent in progress of the thermotherapy treatment, the temperature probe which carries the temperature sensors should project into the prostate gland or other treated tissue at a particular location and at an anticipated angular relationship to the urethra. With the temperature probe penetrating into the prostate gland at the anticipated location and angle, the temperature sensors occupy a predetermined relationship with the SAR energy pattern radiated into the prostate gland. That predetermined relationship permits the temperature readings to be used for reliable calculations of the extent and progress of the tissue necrosis as well as the temperature distribution within the prostate gland as the treatment progresses. If the temperature probe penetrates into the adjoining tissue at an unanticipated angle, the information derived concerning the progress of the treatment is not as accurate.
To establish the predetermined location for insertion of temperature probe, a typical inflatable balloon is located at the forward or distal end of the catheter. The catheter is inserted from a proximal exterior location of the patient through the urethra until the balloon is located within the bladder. To be inserted through the full length of the urethra into the bladder, the catheter must be made of relatively flexible materials. Once the distal end is positioned in the bladder, the balloon is inflated, and the catheter is pulled proximally or outward to seat the inflated balloon against the neck of the bladder. A probe guide tube for the temperature probe extends from the proximal end of the catheter to a location proximally spaced from the balloon. The temperature probe moves through and out of the probe guide tube and into the prostate tissue at the location proximally spaced from the balloon where the probe guide tube opens into the side of the catheter. Thus, the location where the temperature probe penetrates the tissue is established by the relationship of the distal end of the probe guide tube within the catheter relative to the balloon.
The angle which the temperature probe penetrates into the adjacent tissue is established by the angle of the probe guide tube at its distal end relative to the axis of the catheter. The catheter includes structural elements to maintain the probe guide tube at the predetermined angle. However, because the catheter must be made of flexible materials to permit insertion within the urethra, the structural elements for supporting an orienting the distal end of the probe guide tube at the predetermined angle must also be also somewhat flexible. The flexibility of the guide support structural elements can cause unintended variations in the penetration angle of the temperature probe. Maintaining the angle of the distal end of the probe guide tube is also somewhat complicated by the relatively narrow transverse width of the catheter itself. The relatively narrow transverse width tends to limit the degree of angulation of the probe guide tube near its distal end relative to the axis of the catheter. The limitation on the degree of angulation has the effect of exaggerating variations in the penetration angle which result from relatively small influences of flexibility of the catheter. While different probe guide tube support structures have been devised to attempt to preserve the predetermined angular relationship of the distal end of the probe guide tube, those structures must not significantly interfere with the flexibility of the catheter, because flexibility is required for inserting the catheter in the urethra.
Maintaining the angular orientation of the distal end of the probe guide tube is also complicated by a hollow concentric chamber or passageway which surrounds the coaxial cable that feeds microwave energy to the antenna. Inherent and unavoidable energy losses in the coaxial cable extending between the microwave generator and the microwave antenna have the potential to generate enough heat from the coaxial cable to damage the healthy tissues in the urethra and penis which are adjacent to the coaxial cable. To eliminate or reduce the risks of this undesirable heat transfer and damage to healthy tissue, cooling liquid is circulated around the coaxial cable. Circulating cooling liquid around the coaxial cable removes the heat generated by the losses in the coaxial cable and prevents undesired damage to the surrounding healthy urethra and penis.
On the other hand, it is desirable to concentrate as much heat is possible at the location where tissue destruction is desired. To this end, circulating cooling liquid around the microwave antenna is to be avoided. Instead, the heat generated by the microwave antenna should be confined within the catheter at that area so that the heat can transfer by conduction and convection into the adjoining tissue, thereby facilitating the necrosis of that tissue. The above-noted U.S. Pat. No. 6,584,361 describes the advantages of separating the cooling liquid from the heated liquid surrounding the microwave antenna. It is desirable to have the liquid surrounding the microwave antenna because the liquid more effectively matches impedance at microwave frequencies to obtain greater transmission of the microwave energy radiated from the antenna into the surrounding tissue. Since the surrounding tissue is predominantly liquid, liquid surrounding the microwave antenna provides a more continuous medium and impedance for the transfer of the radiation, than would occur if a gap or a significant amount of different type of material surrounded the microwave antenna.
The type of catheter described in the above-noted U.S. reissue Pat. No. Re 38,299 permits liquid to surround the microwave antenna but confines the circulation of cooling liquid to an area along the coaxial cable. A concentric chamber surrounds both the microwave antenna and the coaxial feed cable, but the circulation path is established only through that portion of the concentric chamber that surrounds only the coaxial feed cable. A hole extends through a tube within which the antenna and attached coaxial cable are inserted in the catheter, and the hole is located at a position proximal from the antenna at the coaxial cable. The cooling liquid enters the concentric chamber at the proximal end of the catheter, flows distally in the chamber to the location of the hole, flows through the hole, and then flows proximally in a passageway along the coaxial cable to the proximal end of the catheter. The part of the concentric chamber adjacent to the microwave antenna becomes a still liquid chamber, because liquid at that part of the concentric chamber is not within the flow path established by the location of the hole. Instead of circulating, the water in the still liquid chamber heats to a significantly higher temperature than the circulating liquid. The significantly higher temperature transfers desirable amounts of thermal energy into the adjacent tissue to assist the radiated energy in creating tissue necrosis. The heated still liquid facilitates the transfer of microwave radiation energy by establishing a continuous medium of more closely matched impedance characteristics between the antenna and the tissue.
It is with respect to these and other background considerations that the present invention has evolved.